1. The Field of the Invention
This application relates generally to drilling methods and devices used in drilling. In particular, this application relates to methods and apparatus for reducing unintended egress of drilling tools from a borehole during a drilling operation.
2. The Relevant Technology
Many drilling processes are currently known and used. One type of drilling process, exploration drilling, often includes retrieving a sample of a desired material from a formation. In a conventional process used in exploration drilling, an open-faced drill bit is attached to the bottom or leading edge of a core barrel for retrieving the desired sample. The core barrel includes an outer portion attached to the drill string and an inner portion that collects the sample. The drill string is a series of connected drill rods that are assembled section by section as the core barrel moves deeper into the formation. The core barrel is rotated and/or pushed into the desired formation to obtain a sample of the desired material (often called a core sample). Once the core sample is obtained, the inner portion containing the core sample is retrieved by removing (or tripping out) the entire drill string out of the hole that has been drilled (the borehole). Each section of the drill rod must be sequentially removed from the borehole. The core sample can then be removed from the core barrel.
In a wireline exploration drilling process, the core barrel assembly (or other drilling tool) is positioned on a drill string and advanced into the formation. The core barrel assembly includes an outer portion and an inner tube assembly positioned within the outer portion. The outer portion of the core barrel again is often tipped with a drill bit and is advanced into the formation. However, the inner tube assembly of the core barrel often does not contain a drill bit and is not connected to a drill string. Instead, the inner tube assembly is releasably locked to the outer portion and the entire core barrel assembly is advanced together. When the core sample is obtained, the inner tube assembly is unlocked from the outer portion and is retrieved using a retrieval system. The core sample is then removed and the inner tube assembly placed back into the outer portion using the retrieval system. Thus, the wireline system reduces the time needed to trip drill rods of a drill string in and out when obtaining a core sample because the wireline system is used instead.
In some drilling processes, a horizontal or above horizontal borehole is drilled in an upward direction. In such processes using a wireline system, the inner tube assembly is pumped into place using a valve and seal portion on the core barrel assembly by applying hydraulic pressure behind the seal portion, thereby forcing the inner tube assembly into the upwardly oriented borehole. Once the inner tube assembly is in position and locked to the outer portion, the hydraulic pressure is removed and the core barrel assembly advanced. To retrieve the inner tube assembly, a wireline may be pumped into the borehole in a similar process, and the inner tube assembly uncoupled and removed as described above.
While such a process can reduce the time associated with retrieving core samples, difficulties can arise in removing the inner tube assembly. For example, occasionally the inner tube assembly can fall out of the drill string, causing potential hazards to equipment and personnel at the surface as the core barrel assembly exits the borehole at potentially a high velocity.